Cool, but what about the cost of opportunity? Instead of doing a doctoral program one could be working all those years as a masters which is not bad at all 
I don't know, but I think that for most cases getting a PhD is not a good idea money wise. But of course if it is what you love to do then go for it. 
You have to remember most PhD students have the tuition waived by working as teaching or research assistants, plus you get a small salary as well ($20,000 per year approx.) so its really not as bleak as you think. I was also lucky because I had worked for a while beforehand so I had money saved up plus my wife was working full time while I was doing the PhD, as well as the money I was getting for being a research assistant, so we were living quite comfortably during that time.
If you want to be a college professor at a private university, most won't look at you without both a PhD and an exceptional resume of research. Granted, depending on the discipline, you can teach without having a PhD, but it sure helps if your trying to land a spot within Academia.
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That's a very important point, most people that do a PhD do so to teach at a university. I'm an anomaly in that I went into the corporate world, which is really very very rare.
In what field?
I live in Silicon Valley loll so you can probably guess I work in IT (software development). But my PhD is in industrial engineering
